Tool with an electric motor as its drive The invention relates to a tool, in particular to a garden tool, e.g. a lawnmower, with an electric motor as its drive and an exchangeable, rechargeable battery, the electrical terminals of which can be connected via a plug device to the motor terminals.
In small, battery-operated electric tools, for example hand drills or hand held screwdrivers which are operated by electric motors, it is customary to provide a battery pack which is equipped with plug-in contacts which can be plugged into mating terminals on the electric hand held tool or on a charging appliance. In this case, the plug-in contacts and the mating terminals each form part of a plug coupling, some of the connection means comprising contact pins which project in the plug-in direction.
A battery pack of this kind for electric hand held tools is known from DE 94 21 382. In this case, in addition to the plug-in contacts which make the electrical connection to the drive motor or to the charging appliance, form-fitting connections which rule out polarity reversal are also provided. In the case of the known battery pack, electrical connection is inevitably made when putting the coupling parts together. In order to prevent unintentional short-circuiting of the battery pack which is isolated from the hand tool, the coupler connections of this kind cannot readily be employed because safety considerations dictate that it is necessary to provide an additional switch to interrupt the flow of current in the immediate vicinity of the battery, in order to make the tool childproof.
Lawnmowers with exchangeable battery packs in which terminals are arranged on the outside of the battery pack are known, which terminals, when the battery pack is inserted into a battery guide in the casing of the tool inevitably makes contact with the terminals situated in the tool. A switch, which is generally designed as a detachable-key switch, is provided as a safety switch on the lawnmower chassis in the vicinity of the battery. To recharge the battery, terminals for the insertion of a socket connector are provided in the tool casing via which connector a charging appliance supplies current to recharge the battery. The battery can also be recharged after it has been removed from the tool, using the charging appliance which can be connected to the battery terminals.
In the case of a tool which is described in WO 94/01993 and is designed as a lawnmower, the bow plug is designed as an overload protector and contains either a fuse or an overload circuit breaker. The battery pack, which in the known tool is installed fixedly in the chassis, has a charging plug, a power transformer and a rectifier which is connected to the battery. The charging plug is connected to the mains in order to recharge the battery. The sockets of the mains plug can only be pushed onto the charging plug pins when a slide lying above them has been displaced laterally, and its displacement into the open position is only possible when the bow plug has been pulled off the battery terminals, thus isolating the motor from the battery terminals. As long as the slide is in the displaced position, releasing the mains connection, the safety bow plug cannot be plugged in, so that the connection between motor and battery remains interrupted as long as the mains plug is connected to the tool.